Polygonal darkness appearing in render
Two ways to solve this

1  scale down the space_backdrop sphere so it fits inside the camera clipping bounds

2
Set the viewing mode to shaded (press Z again), and you can clearly see it's not a shadow but a feature of the clipping plane. Modify the Clipping End parameter (In Properties > Camera Settings) to be large enough to fit the whole scene.





it's difficult to see in wireframe mode:


to visualize the clipping plane, you enable 'limits' in the Display panel of the camera. View the scene from the side and zoom out to see how the limits indicator behaves as you adjust the End value